Ok Tech, im stumped and need some help.

Car Details
-LS1/60e 99 Camaro
-Stock Bottom end
-Fast 92 intake & TB
-Delphi 85mm MAF
-LS7 Lifters
-Cometic .040 Head gaskets
-BTR 7.4" Pushrods
-FTI Street Sweeper HT Cam( 228/232 .600/.612 111 LSA)
-Unmodded TBSS 243s w. BTR .660 springs
-GTP Injectors, walbro 255
-TR55 plugs

Ive put this car together over the past year, and a few weeks ago it started for the first time. Had my friend who tunes come over with his computer(used HP tuners) and make sure everything was online. On its first fire it started right up. Turned it off after a second or 2 because the cluster wasnt hooked up, so no way to see if it had oil pressure. Didnt want to chance it. Wanted to start it up again to get that "Project car finally starts vid" so i tried to start it again. fired right up without a hiccup, turned the key and shut her off.

Fast forward 2 days later and i finish getting the exhaust on the car and installing the dash so i have gauges. Try to fire and its cranks for a few seconds before no lie the loudest backfire i have ever heard out of a NA car lol It shook the dust off the ceiling and walls in my garage. Had my friend with HP tuners come back over to see if something was up. Cranked over a few times and let a fairly large backfire out of the throttle body. Big enough that there was smoke. At that point it was time to investigate.

Pulled the plugs, found the following:

Cyl 1



Cyl 3



cyl 5



cyl 7



cyl 2



cyl 4



cyl 6


cyl 8


As you can see, 3 and 5 look brandy new. Barely smelt like fuel, and were just slightly damp.

Thought: No Spark on 3 and 5

Pulled the plugs and grounded them to the block. Cranked the motor and sure enough, spark. On tho the next..

Thought: Mistmatched Coil Harness

Pulled the Coil harnesses off the car just to verify i have them in the right firing order. I believei have them correct.

1-Red
2-Red
3-Green
4-Green
5-Blue
6-Blue
7-Purple
8-Purple

Thought: Bad Injectors

Swapped out the set of GTP injectors i had(purchased used from another member) in the car for the stock ones that came out of the car, a known working set. Loaded up a new file into the pcm and gave it a go.

Slight improvment. The car will start if i nurse the throttle, once started it doesnt want to stay running, and begins to pop/backfire. As seen in the youtube vid linked below...


Thought: Compression Test

Without much more i could think of, i figured the next logical step would be a compression test. Using a SnapOn compression tester, cranked the motor for 4 "jumps" of the gauge as per instructions. Fuel pump off and coil packs unplugged, so no fuel or spark. Cold engine obviously.

1- 95
3- 98
5-100
7-98

2-87
4-85
6-90
8-98

Clearly not good ! lol

Thought: Timing Off

If the timing is a tooth or 2 off, valves may be a bit open when they should be closed, possibly effecting my compression. So the tear down continued, pulled the cover and verifed the timing is indeed mark to mark, 6 to 12.



Low compression across the board has my super confused. My only real guess is the pushrods are a hair to long and keeping the valves slightly open. It is possible it is rings, but the motor was running fine before the cam and head swap. So seems odd that it would need rings all of a sudden.

Todays plan of action is measure pushrod length, and if results match to the 7.4" that are in the car, then a leak down test is next.

 

did a leak down test last night on cyl 1. did it 4 different variations as youll see below.

Dot to dot, push rods installed. rockers not torqued but seated onto the rocker tray.


[url=https://flic.kr/p/DjzwnG]



cam gear at 12, crank gear at 12, pushrods and rockers same as previous.

[url=https://flic.kr/p/21sghD2]

Dot to Dot, no pushrods or rockers.

[url=https://flic.kr/p/21sghzp]

12 and 12, no rods or rockers.

[url=https://flic.kr/p/21pxqxL]

All 4 tests pass. Air could be heard hissing from the crank case(i dont have the timing cover on) but the gauge says its only 14-16% loss, which passes. unless im understanding it wrong.

 

No one has any recommendations ?

 

 

both sub harness go on the same way, so it should be red 7 and 2, if I'm remembering red right correctly. I have it written on the shop wall I no longer build the coil racks.

 

 

I guess I'm saying the obvious here but those blackened spark plugs will likely be the source of your misfire. Looks like a rich fuel deposit on the porcelain, probably not oil. Bad injector spray pattern in those cylinder??

Rick

 

i think u should check your pr length as well. i just wrapped up my build waiting on a tune and i think my rods are correct. little sewing machine noise and car seems to drive ok.

but i used unmilled 799s and stock GM MLS gaskets which are thicker than your .040s and i came up with a 7.3 rod somehow. i am running lash caps tho and morel lifters, and im still on the high side of preload for the morels at just under 1 rocker bolt turn for roughly .070 preload. why not try buying some 7.35 rods in the classifieds, swap them in, then try your compression test again?